Author: Conor Graff
North Pacific Krill
By Conor Graff
Common Name: North Pacific Krill
Scientific Name: Euphausia pacifica
Size range: Between 16 and 25mm
The North Pacific Krill is an ocean-based crustacean that can grow up to 25mm in length (this is a bit of a stretch, however; most average around 16mm). The word Euphausia is Latin for ‘brightly shining’, and indeed, these small invertebrates are noted for what appears to be a bioluminescent characteristic throughout their species. North Pacific Krill have large black eyes and large abdomens, and closer inspection reveals what appear to be gills formed around their legs, and scales on their antennae (these scales are very large and used to protect their antennae from damage).
The North Pacific Krill live, as their name would suggest, on the ocean of the same name. This stretch in habitat runs from the southernmost coasts of the US all the way to Japan, and due to their instincts to band into close ‘clouds’ of themselves, they can cover large areas as a quasi-community without having to move from one place to another. However, the accumulation of these krill is anything but organized; while krill can accumulate into these areas of themselves, they usually form these clusters in areas that would be the most hospitable. The gist is that these krill can be found in very large quantities around the stretch that is their habitat, while other areas are completely barren of krill.
Krill tend to dwell in the ocean’s “twilight zone” (the area between the ‘surface zone’ and the ‘bottom zone’), wherein they can stay out of the reach of most surface zone-dwelling predators. Krill swim to the surface zone during the night, where, under cover of darkness, they can find and feast on their food source, phytoplankton.
As mentioned above, krill feed mostly on phytoplankton (“plant plankton”), making them herbivorous. They feed via a complicated system in their mouthparts wherein the phytoplankton is filtered out of the water into the krill’s jaws.
Krill do not feed exclusively on phytoplankton; many are omnivores who feed of animal plankton (zooplankton). As mentioned before, Krill only come out at night to feed (all the better in escaping from hungry predators).
Krill are perhaps the richest form of protein in the entire ocean, which may be why a certain surface-dwelling species (humans) have discovered and started harvesting them.
They tend to be a primary diet of baleen whales and a number of fish (notably salmon); however, humanity has begun to take an interest in these small creatures. In BC, krill are fished out in large quantities in order to feed aquariums, fish farms, and ourselves; Japan is also immensely interested. Those who have tried krill tend to say it has no taste when fresh and raw; however a bitter, powerful flavor is created from krill that is dried out in the sun or frozen.
Krill reproduction starts out in a familiar way to nearly every living creature: that with the release of sperm. Upon receiving the male Krill’s sperm, females store the semen in their bodies and fertilize them, and proceed to release the eggs that come out of this union. A female can release up to 20 000 eggs at a time in clusters with intervals in between. The eggs are laid several hundred meters in the twilight zone, where the larvae can safely hatch without being attacked by most day-dwelling creatures. Upon hatching, krill larvae feed of the nutrients given by the egg yolk. Larvae soon develop through many stages in order to finally reach their adulthood.
European Green Crab
Common name: European Green Crab
Scientific name: Carcinus maenas
The European Green Crab is commonly between 60mm long and 90mm wide but has been noted to grow up to 101mm wide in non-native areas such as British Columbia.
The European green crab is not always pure green, its dorsal shell being mottled dark green to brown with yellow patches on the ventral surface. However, the crab’s shell may change to orange or red during the molting cycle. Some of the most identifiable features of the Carcinus maenas are the array of five spines on either side of the eyes on the front end of the carapace, and three rounded bumps between its eyes.
European Green Crabs are an invasive alien species that originated in the Baltic Sea, in the Atlantic Ocean off the coast of Western Europe and Northern Africa. It is believed they first came to North America in the 1800’s in the dry ballasts or ballast water of large ships. They first became established on the west coast of North America in Central California near California. Though most invasive species in British Columbia are thought to come in ballast water of visiting ships it is thought the Green Crab most likely arrived as larvae that drifted on northern currents from the central California area. They can now be found from Central California all the way up to Southern British Columbia. Green Crabs are very adaptive and can tolerate a wide range of salinity (4-54 ppt) and temperatures (0-33°C). Green Crabs can be found in a variety of habitats in the intertidal zone such as: protected rocky shores, cobble beaches, sand flats, and tidal marshes.
The European Green Crab will feed on anything it can get its claws on, its most common prey being: clams, oysters, mussels, and other small native crabs. The crab is extremely dexterous, and has many ways to open the shellfish it eats.
In its native habitat Carcinus maenas’ predators include the Conger Eel, the Trigla Lucerna, Bass, and the Fivebeard Rockling. The crab’s defenses include its ability to rotate its claws over its back to defend against predators coming from behind, and being able to live outside of water in the sun for up to a week.
Reproduction & Life Cycle:
European Green Crabs typically mate during the summer, when the female crab has just molted and is vulnerable. During this time, the male green crab guards the female by pairing with her in a “pre-molt cradling”, protecting her from other males and predators. The egg sac appears a few months after mating and is carried for several months. The eggs then hatch into free-swimming larvae that stay in the water for 17 to 80 days before settling to the bottom as tiny crabs. The European green crab lives for up to five years and reaches sexual maturity at two or three years.
Known as The Most Invasive Crab in the World, the European Green Crab is a huge threat to our waters. Its floating larval stage contributes largely to its rapid migration and its feeding habits and environmental tolerance enables it to adapt to many places. Marine biologists believe the crab will also wipe out many commercial fish after already being discovered as a leading natural contributor to the dramatic declines in soft-shell clam fishery (aided by its ability to consume over 40 small clams a day). Also a threat to vital Eel-Grass habitats for many small creatures, the crab will snap the plants at their base, effectively preventing the grass from growing and reproducing.
Interesting resources for research and photographer credit
Victoria High School
1260 Grant St.
Victoria. BC, Canada